The overall objective of the proposed research is to understand how the product of the src gene of Rous sarcoma virus, a representative retrovirus, is responsible for the initiation and maintenance of the transformed state. The functions specified by the src gene will be analyzed through the use of conditional lethal and deletion mutants. Using antisera to the src gene product (called p60src) we will purify it from several different types of virally transformed cells. The physical and chemical properties of the different src gene products will be compared. We intend to localize p60src in transformed cells by indirect immunofluorescence, immunoelectron microscopy, and subcellular fractionation. The presence and amount of p60src will be correlated with various parameters of the transformed phenotype. Investigations of contractile proteins of normal and virally transformed cells will be continued.